Change bitcoin-util-test.py to use Python3

Author: jnewbery

src/Makefile.test.include

@@ -147,7 +147,7 @@ bitcoin_test_clean : FORCE
 
 check-local:
 	@echo "Running test/util/bitcoin-util-test.py..."
-	$(PYTHON) $(top_builddir)/test/util/bitcoin-util-test.py
+	$(top_builddir)/test/util/bitcoin-util-test.py
 	$(AM_V_at)$(MAKE) $(AM_MAKEFLAGS) -C secp256k1 check
 if EMBEDDED_UNIVALUE
 	$(AM_V_at)$(MAKE) $(AM_MAKEFLAGS) -C univalue check

test/util/bitcoin-util-test.py

@@ -1,9 +1,8 @@
-#!/usr/bin/env python
+#!/usr/bin/env python3
 # Copyright 2014 BitPay Inc.
 # Copyright 2016 The Bitcoin Core developers
 # Distributed under the MIT software license, see the accompanying
 # file COPYING or http://www.opensource.org/licenses/mit-license.php.
-from __future__ import division,print_function,unicode_literals
 import os
 import sys
 import argparse